1. Field of the Invention
This invention is concerned with manufacture of high grade viscous oil products from crude petroleum fractions or other hydrocarbon materials. It is particularly directed to the manufacture of high quality lube basestock oils from crude stocks of high boiling point as opposed to using so-called light stocks. The latter crudes have lower boiling points and for reasons which are not fully understood, do not show any advantage in the novel process of this invention over commercially practiced technology. More specifically, the invention is concerned with dewaxing of lube basestock oils having an initial boiling point higher than 700.degree. F. and a 50 volume percent boiling point of at least 900.degree. F.
2. Description of the Prior Art
High quality lube basestock oils are conventionally prepared by refining distillate fractions or the residuum prepared by vacuum distilling a suitable crude oil from which the lighter portion has been removed by distillation in an atmospheric tower. Thus, the charge to the vacuum tower is commonly referred to as a "long residuum" and residuum from the vacuum tower is distinguished from the starting material by referring to it as the "short residuum".
The vacuum distillate fractions are upgraded by a sequence of unit operations, the first of which is solvent extraction with a solvent selective for aromatic hydrocarbons. This step serves to remove aromatic hydrocarbons of low viscosity index and provides a raffinate of improved viscosity index and quality. Various processes have been used in this extraction stage, and these employ solvents such as furfural, phenol, sulfur dioxide, and others. The short residuum, because it contains most of the asphaltenes of the crude oil, is conventionally treated to remove these asphalt-like constituents prior to solvent extraction to increase the viscosity index.
The raffinate from the solvent extraction step contains paraffins which adversely affect the pour point. Thus, the waxy raffinate, regardless of whether prepared from a distillate fraction or from the short residuum, must be dewaxed. Various dewaxing procedures have been used, and the art has gone in the direction of treatment with a solvent such as methyl ethyl ketone/toluene mixtures to remove the wax and prepare a dewaxed raffinate. The dewaxed raffinate may then be finished by any number of sorption or catalytic processes to improve color and oxidation stability.
In recent years techniques have become available for catalytic dewaxing the petroleum stocks. A process of that nature developed by British Petroleum is described in the Oil and Gas Journal dated Jan. 6, 1975, at pages 69-73. See, also, U.S. Pat. No. 3,668,113.
In U.S. Pat. No. Re. 28,398 is described a process for catalytic dewaxing with a catalyst comprising zeolite ZSM-5. Such process combined with catalytic hydrofinishing is described in U.S. Pat. No. 3,894,938 for reducing the pour point of a sulfur and nitrogen-containing gas oil boiling within the range of 400.degree.-900.degree. F.
In U.S. Pat. No. 3,979,279, a stabilized lubricating oil stock resistant to oxidation and sludge formation upon exposure to a highly oxidated environment is formed by contacting a high viscosity lubricating oil stock with hydrogen in the presence of a catalyst of low acidity comprised of a platinum-group metal on a solid refractory inorganic oxide support.
In U.S. Pat. No. 3,530,061, a stabilized lube oil product obtained by hydrocracking is produced by contacting a lube oil product before or after dewaxing with a catalyst having hydrogenation-dehydrogenation activity and hydrogen at a pressure in the range from atmospheric up to about 1000 psig under conditions of temperature in the range of 400.degree. F. to about 800.degree. F.
A two-stage process for preparing a high quality lube basestock oil is disclosed in U.S. Pat. No. 4,181,598 in which a raffinate is mixed with hydrogen and the mixture contacted with a dewaxing catalyst comprising a ZSM-5 type catalyst to convert the wax contained in the raffinate to low boiling hydrocarbons and subsequently, contacting the dewaxed raffinate in the presence of hydrogen at a temperature of 425.degree. to 600.degree. F. with a hydrotreating catalyst comprising a hydrogenation component on a non-acid support such as cobalt-molybdate or nickel-molybdate on alumina. Hydrotreating the dewaxed raffinate is limited to saturate olefins and reduce product color without causing appreciable desulfurization.
U.S. Pat. No. 3,755,145 discloses a process for preparing lube oil having low pour points involving using a catalyst mixture comprising hydrogenation components, a conventional cracking catalyst and a crystalline aluminosilicate zeolite of the ZSM-5 type. At Column 8 there is specifically disclosed the use of an extrudate having a 1/16th of an inch diameter.
U.S. Pat. No. 3,894,938 discloses the catalytic dewaxing and desulfurization of gas oils with a ZSM-5 zeolite containing a hydrogenation component. At Column 3 it is specifically pointed out that the ZSM-5 can be incorporated into a matrix and that the catalyst particles can be sized between 1/32nd and 1/8th of an inch.
U.S. Pat. No. 3,846,337 discloses silica-bound silicate particles of improved strength within the range of 1/32 to about 1/8 inch average extrudate diameter and their use in various catalysts reactions.
It has now been found that an improved dewaxing process which exhibits enhanced activity and longer cycle lengths than present commercial dewaxing catalysts may be obtained by utilizing a catalyst composite comprising a crystalline aluminosilicate having a silica-to-alumina ratio of at least about 12 and a Constraint Index of about 1-12 which is dispersed in an inorganic oxide matrix and which optionally contains a hydrogenation component wherein the maximum diffusion distance in the catalyst is less than 0.025 inch and preferably less than 0.02 inch. In the special case of a cylindrical extrudate, the maximum diffusion distance is equal to one-half of the diameter. The diameter of the finished extrudate is less than about 0.05 inch, and more preferably less than about 0.04 inch. A more preferred extrudate size is about 0.03125 inch.
The catalyst form is not limited to extrudates but can be bead shaped, of monolithic support, etc. The extrudate form is not limited to cylinders, but can be triangular, polylobed (e.g. trilobe, quadrulobe, etc.), rectangular, or of other similar form. The extrudate may also contain a central hole lengthwise through the extrudate. Other forms should be equally acceptable. The invention lies in controlling the catalyst's maximum diffusion distance to less than 0.025 inch.